1. Field of the Invention
This invention pertains to apparatus and method useful in the aseptic canning of particulate food material. More particularly this invention relates to apparatus and method for continuously cooking and sterilizing particulate food material without substantially altering its texture, taste and nutritional value.
2. Description of the Prior Art
In the conventional process for canning foods, containers are first filled with food product and sealed. Thereafter, the sealed containers are heated in a pressure cooker or retort to sterilize the canned product. Inadequate preservation of the canned food material's organoleptic quality is one well-recognized problem associated with this approach. To insure that every food piece is adequately sterilized, unavoidable overheating of at least some of the food pieces occurs. This is particularly true when some of the canned food pieces require different heating times to reach sterilization conditions. In particular, those foods requiring less time for sterilization generally tend to be overheated. Heat transfer limitations with the conventional sterilization approach represents still another drawback. Sterilizing food material by transferring heat through both a container and a contained fluid requires more energy than would otherwise be consumed if the canned material were sterilized directly.
Recognizing these limitations, the prior art has proposed procedures for aseptically canning food material. In aseptic canning, food material is sterilized before it is sealed in a container. Generally, food material is quickly heated to sterilization temperatures, typically in the range of 250.degree. F. to 300.degree. F. (120.degree.-150.degree. C.), by direct contact with pressurized steam. The food material is maintained at such temperatures for sufficient time to effect sterilization. Thereafter, the food material is rapidly cooled and the cooled, sterile material is filled into pre-sterilized containers and sealed within a sterile or aseptic environment.
In a particularly efficient and convenient sterilization arrangement, food material is conveyed through a pressurized steam treatment chamber. In this arrangement, heat treatment is controlled simply by controlling the rate food material is passed through the treatment chamber. In order to insure the food material rapidly achieves sterilization temperatures, a temperature in the range of 250.degree. F. to 300.degree. F. (120.degree.-150.degree. C.) must be maintained in the treatment chamber. This condition is obtained using super atmospheric pressure steam, at pressures of, for example, about 10 to about 55 psig.
To date, the basic arrangement for feeding solid particulate food material into and withdrawing it from a pressurized steam treatment chamber involves some type of rotary valve. Both inlet and outlet valves act as seals to maintain pressure with the treatment chamber. One problem with pressure tight rotary valves, however, is that structural degradation of the product often occurs as a result of mechanical abrasion. This is particularly true at the outlet valve where the texture of the food product, to some extent, has been unavoidably impaired by sterilization and is consequently more suseptible to mechanical damage. Another drawback of rotary valves is that at the ever increasing processing speeds demanded by food processors, there often is insufficient residence time within the outlet valve for adequately cooling the food material to a temperature that avoids product flashing. Flashing is caused by rapid vaporization of hot liquid from within the food material caused by its sudden depressurization. Flashing, which tends to disintegrate the solid food particles, can only be avoided by cooling the food material below the atmospheric boiling point of absorbed liquid before depressurization. An improved apparatus and method for removing solid food material from pressurized steam treatment chambers would be very useful to the food processing industry.
It is an object of this invention to provide apparatus and method for removing solid particulate food material from a pressurized steam treatment chamber.
It is another object of this invention to provide apparatus and method for removing solid particulate food material from a pressurized steam treatment chamber while avoiding product flashing.
It is still another object of this invention to provide apparatus and method for removing solid particulate food material from a pressurized steam treatment chamber while preventing its disintegration, attrition and mushing.
Other objects and advantages of the invention will become apparent from the following description.